A. Field of The Invention
The present invention relates to a seal structure, and more particularly to a seal structure for sealing a passage formed between two members.
B. Description of The Related Art
A variety of control valves and the like are typically provided in a control valve body used in an automotive automatic transmission. A separate plate is clamped between an upper valve body and a lower valve body of the valve body within such a transmission. A number of control holes are formed in the separate plate. The control holes are configured to direct fluid to hydraulic circuits defined in the upper and lower bodies. Portions of the hydraulic circuits are in communication with each other through the control holes of the separate plate. Paper gaskets are disposed on each side of the separate plate and are clamped between the separate plate and upper and lower valve bodies. The hydraulic passages formed on sides of the separate plate in both the valve bodies are sealed by the paper gaskets.
In the conventional transmission valve body example described above, portions of the paper gaskets are exposed in some of the hydraulic passages of the control valve body. Because of the exposure to the hydraulic passages, there is a possibility that the exposed portions of the paper gaskets may be degraded by the hydraulic fluid or working oil within the transmission valve body. Degraded paper gasket material eventually may become suspended in the working oil and may subsequently clog an important fluid passage or orifice within the transmission valve body. Also, the paper gaskets may expand when exposed to vacuum pressure generated in the hydraulic passages reducing the flow of working oil in the passages.
Japanese Patent Application Laid-Open No. Hei 7-71607 discloses a seal structure in which a seal portion is formed on the separate plate by a pattern printing process. Complicated shapes may be realized by using pattern printing methods thus forming a seal portions which conforms to the shape of an end face of the valve body. Namely, the seal portions are designed to avoid being exposed to portion of the hydraulic passages of the valve body that are in communication with sensitive control valves in the valve body thus minimizing the possibility of degradation or peeling of the seal portions that may obstruct the operation of the control valves.
In the seal structure disclosed in Japanese Patent Application Laid-Open No. Hei 7-71607, the various portions of the seal portions are formed to have substantially the same width as corresponding portions of the end face of the valve body. Namely, those portions of the seal portions corresponding to narrow portions of the valve body end face are formed to have a narrow width and those portions of the seal portions corresponding to wide portions of the valve body end face are formed to have a wide width. Since the width of the seal portions varies, and, for example, the liquified seal agent is applied by the screen printing, there may be a non-uniformity in thickness in various portions of the seal portions having differing widths due to surface tension effects. If such a non-uniformity in thickness is generated, the sealing function may be degraded. Furthermore, if the seal portions are formed across the entire width corresponding to the end face of the valve body, the amount of the seal material would be increased. As a result, the cost for the unit of the separate plate and seal portions may be undesirable.